This invention relates spread-spectrum communications, and more particularly to code-division-multiple-access (CDMA) cellular, collision detection for packet-switched systems.
Presently proposed for a standard is a random-access burst structure which has a preamble followed by a data portion. The preamble has 16 symbols, the preamble sequence, spread by an orthogonal Gold code. A mobile station acquires chip and frame synchronization, but no consideration is given to closed-loop power control or collision detection.
An objective is to provide random channel access with reliable high data throughput and low delay on CDMA systems.
Another object of the invention is to maintain reliability for high data throughput and low delay on CDMA systems.
According to the present invention, as embodied and broadly described herein, an improvement to a code-division-multiple-access (CDMA) system employing spread-spectrum modulation, is provided. The CDMA system has a base station (BS) and a plurality of remote stations. The base station has BS-spread-spectrum transmitter and a BS-spread-spectrum receiver. Each of the plurality of remote stations has an RS-spread-spectrum transmitter and an RS-spread-spectrum receiver. The method comprises the steps of transmitting from the BS-spread-spectrum transmitter, a broadcast common-synchronzation channel having a common chip-sequence signal common to the plurality of remote stations. The broadcast common-synchronization channel has a frame-timing signal.
At a first RS-spread-spectrum receiver, the steps further include receiving the broadcast common-synchronization channel. From the broadcast common-synchronization channel, the steps include determining frame timing at the first RS-spread-spectrum receiver from the frame-timing signal.
From a first RS-spread-spectrum transmitter, the steps include transmitting an access-burst signal. The access-burst signal has a multiple segments at different power levels, that is to say typically at sequentially increasing power levels.
The BS-spread-spectrum receiver receives at least one segment of the access burst signal at a detectable power level. In response, the BS-spread-spectrum transmitter sends an acknowledgment signal back to the first RS-spread-spectrum receiver. Receipt of the acknowledgment signal by the first RS-spread-spectrum receiver causes the RS-spread-spectrum transmitter to send data to the BS-spread-spectrum receiver. The detection of the segment at an adequate power level, acknowledgment communication and subsequent data transmission provides the remote station (RS) with random access to the channel (RACH).
The preferred embodiment also provides that when there is a collision of a first access-burst signal with a collision access-burst signal, then the BS-spread-spectrum receiver does not correctly receive the collision-detection portion of the first access-burst signal. Thus, the BS-spread-spectrum transmitter transmits to the first RS-spread-spectrum receiver, an collision-detection without reflecting the collision-detection portion. At the first RS-spread-spectrum receiver, in response to receiving the collision-detection signal without the collision detection portion, the first RS-spread-spectrum transmitter transmits to the BS-spread-spectrum receiver, a second access-burst signal.
Additional objects and advantages of the invention are set forth in part in the description which follows, and in part are obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention also may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.